Abstract away InstanceCopyPrefs' internals through new getSelectedFiltersAsRegex() function

+ fix typo in comment
+ remove unused import
+ add [[nodiscard]] to methods

Signed-off-by: Marcelo Hernandez <marcelohdez.inq@gmail.com>

launcher/InstanceCopyPrefs.cpp

@@ -14,3 +14,36 @@ bool InstanceCopyPrefs::allTrue() const
         copyServers &&
         copyMods;
 }
+
+// Returns a single RegEx string of the selected folders/files to filter out (ex: ".minecraft/saves|.minecraft/server.dat")
+QString InstanceCopyPrefs::getSelectedFiltersAsRegex() const
+{
+    QStringList filters;
+
+    if(!copySaves)
+        filters << "saves";
+
+    if(!copyGameOptions)
+        filters << "options.txt";
+
+    if(!copyResourcePacks)
+        filters << "resourcepacks" << "texturepacks";
+
+    if(!copyShaderPacks)
+        filters << "shaderpacks";
+
+    if(!copyServers)
+        filters << "servers.dat" << "servers.dat_old" << "server-resource-packs";
+
+    if(!copyMods)
+        filters << "coremods" << "mods" << "config";
+
+    // If we have any filters to add, join them as a single regex string to return:
+    if (!filters.isEmpty()) {
+        const QString MC_ROOT = "[.]?minecraft/";
+        // Ensure first filter starts with root, then join other filters with OR regex before root (ex: ".minecraft/saves|.minecraft/mods"):
+        return MC_ROOT + filters.join("|" + MC_ROOT);
+    }
+
+    return {};
+}